This section introduces aspects that may help facilitate a better understanding of the invention. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is prior art or what is not prior art.
Consider the following scenario. A base station (BS) is equipped with M (typically from 4 to 20) antennas and should transmit data to K (typically from 10 to 40) users. Wireless base stations with many antennas are a strong candidate for future generations of wireless networks, offering very significant increases in data rates. One possible implementation of such systems can be obtained by configuring several light radios (small basic radio with a single antenna) together.
The wireless channels between the BS and K users stay approximately constant during coherence intervals of length T seconds (typically T is about half a millisecond). The channel between the BS and a user changes significantly from one coherence interval to the next. Such changes take place about 2000 times/sec. Therefore, the channel between the BS and a user could have very high throughput during coherence interval 1 and very bad throughput during coherence interval 2.
In the beginning of each coherence interval, the BS chooses a new subset of L users whose channels have the highest throughputs. The BS then transmits data only to those L users. This approach allows one to maximize the system throughput.
The problem, however, is how to inform each user whether it was selected or not for data transmission in a particular coherence interval. One known solution is to send to each user a dedicated signal indicating whether the user is selected or not. This solution has at least two substantial issues though.
1. The dedicated signals should be transmitted to the users very reliably. Otherwise, an unselected user can assume that data is being transmitted to it during a particular coherence interval. As a result, packet synchronization can be lost, which leads to serious service degradation. The opposite possibility can also occur—a selected user fails to receive a packet when it should. To avoid these problems the selection error probability should be of the order of 10^(−7). This means that dedicated signals must have long duration to be received reliably.
2. Since the coherence intervals are short, transmission of these dedicated signals occupies almost the entire coherence interval. This means significant system throughput degradation.
Thus, new solutions and techniques that are able to address some of the issues with coherence interval user selection would meet a need and advance wireless communications generally.
Specific embodiments of the present invention are disclosed below with reference to FIGS. 1-2. Both the description and the illustrations have been drafted with the intent to enhance understanding. For example, the dimensions of some of the figure elements may be exaggerated relative to other elements, and well-known elements that are beneficial or even necessary to a commercially successful implementation may not be depicted so that a less obstructed and a more clear presentation of embodiments may be achieved. In addition, although the logic flow diagrams above are described and shown with reference to specific steps performed in a specific order, some of these steps may be omitted or some of these steps may be combined, sub-divided, or reordered without departing from the scope of the claims. Thus, unless specifically indicated, the order and grouping of steps is not a limitation of other embodiments that may lie within the scope of the claims.
Simplicity and clarity in both illustration and description are sought to effectively enable a person of skill in the art to make, use, and best practice the present invention in view of what is already known in the art. One of skill in the art will appreciate that various modifications and changes may be made to the specific embodiments described below without departing from the spirit and scope of the present invention. Thus, the specification and drawings are to be regarded as illustrative and exemplary rather than restrictive or all-encompassing, and all such modifications to the specific embodiments described below are intended to be included within the scope of the present invention.